Cobalt is one candidate for a new material solution for both contact and BEOL (back end of the line) interconnect fill applications in 10/7 nm nodes. Tungsten (W) contacts include a titanium (Ti)/titanium nitride (TiN) barrier which the inventors have observed is problematic as the Ti/TiN barrier increases interface resistance and limits downward scaling of features (e.g., interconnects). Additionally, the inventors have observed copper (Cu) vias are problematic when a barrier/liner increases interface resistance and negatively impacts via resistance scaling.
Further, the inventors have observed that conformal cobalt fill by chemical vapor deposition (CVD) often undesirably results in voids embedded into the feature, and forms micro-voids. Even using an aggressive anneal process (e.g., higher temperatures and longer anneal times), the micro-voids are difficult to remove and may undesirably remain in the feature. Moreover, the BEOL process includes limited anneal temperatures to protect the dielectric materials on the substrate.
Accordingly, the inventors have provided an improved method for filling substrate features with cobalt.